The present invention relates to a composite pipe, process for producing the same, and a heat pipe using the same.
Aluminum is high in electric conductivity, non-magnetic, high in heat conduction, and light in weight, and also has excellent ductility and malleability, and easy for continuous extrusion. It has recently been used e.g. as a metal sheath of long electric power cables for the sake of these advantages.
Aluminum pipes are continuously extruded by means of a continuous extrusion machine which can extrude while enveloping a long object. Thus, long seamless pipes can be produced. Besides, since the material itself is soft, pipes of a small diameter are flexible without corrugation, and can be transported by winding around a drum. Also, the pipes of a large diameter can be easily corrugated, and can be easily wound around a drum or laid at winding places. Furthermore, a considerable maximum tensile stress can be expected for aluminum, though not as high as that of iron, and it is possible to obtain pipes which can withstand a considerably high internal pressure.
However, aluminum pipes are inferior in corrosion resistance without particular anticorrosive treatment can be easily attacked by water, steam or methanol, and the abovesaid advantages cannot be fully exhibited. For instance, aluminum pipes are not generally used for transportation of water, steam or chemical solutions such as methanol. If aluminum pipes are used for heat pipes with water or methanol used as the working fluid because of their high heat conduction, low price and safety, hydrogen gas may be generated due to reaction between this working fluid and aluminum after lapse of a long time. Thus, the working fluid is limited to Freon or the like.
On the other hand, lead is a very stable metal against corrosion, and resists water, steam and many chemicals. Lead is also high in conductivity, non-magnetic, high in heat conduction, rich in ductility, malleability and flexibility, and is applicable to long extrusion process. To the contrary, it is too soft and is poor in maximum tensile strength, which means that it cannot be used at high pressure when produced into pipes. Besides, it is very heavy. Hence, when it is used as pipes, its use has been extremely limited.
An object of the present invention is to provide corrosion resistant long composite pipes having both the advantage of lead and that of aluminum.
Another object of the present invention is to provide a process for producing such composite pipes.
A further object of the present invention is to provide a heat pipe with which water and methanol can be used as working fluid by using the composite pipe.
The term "a continuous extrusion machine which can extrude while enveloping a long object" means, in the case of aluminum, e.g. an aluminum press for metal extrusion of power cable manufactured by Hydraulik GmbH of Germany and an aluminum press manufactured by Schloemann GmbH of Germany, and in the case of lead, means e.g. a so-called vertical lead encasing machine and a screw extrusion type machine widely used to produce a metal sheath of power cable, generally known as the Hansson type lead encasing machine.